1. Field of the Invention
This invention is directed to an insulation displacement contact intended for use in making an electrical termination to round conductor and is more particularly related to two insulation displacement contacts especially adapted for making an electrical termination to wires of different sizes in the same hybrid flat cable.
2. Description of the Prior Art
Insulation displacement contacts, or slotted plate contacts have been reliably used to established electrical connection with both discrete conductors and conductors employed in a flat cable. A parallel plate configuration having a dual slot feature, in which aligned slots are formed in two parallel plates is often employed with discrete wires. These dual slots may both be electrical contact slots or one may function as an insulation support or strain relief. Such dual slot insulation displacement contacts can enhance electric performance if one of two primary electrical contact slots undergoes degradation in performance, because the other provides a redundant contact. An insulation strain relief function, which can be provided by one slot, can prevent mechanical forces from being transferred to the active electrical contact.
When insulation displacement slotted contacts are employed with flat cable, dual slotted configurations or parallel plate configurations are generally not employed. Typically, a single slot feature is employed in a connector used to form an insulation displacement mass termination of flat or ribbon cable. These single slot contacts typically have sharp or pointed beam tips intended to penetrate cable jackets and allow entry of the conductors into the slot. U.S. Pat. No. 4,460,228 discloses one such electrical connector intended for establishing an insulation displacement termination with a plurality of conductors in a flat cable. Other such configurations are shown in U.S. Pat. No. 4,077,695 and U.S. Pat. No. 4,691,977. These patents are merely representative of a number of different configurations which employ sharp points on the tips of insulation beam contacts to penetrate the insulation in a flat cable.
A typical flat cable of the type with which these contacts are employed has a plurality of spaced apart round conductors, which are embedded in a laminated or extruded insulation web. Typically, the extruded flat cable configurations or ribbon cables, have an extrusion of substantially the same thickness encasing all of the conductors in the ribbon cable. Typically these conductors are the same size and are spaced apart by sufficient distance so that a flat section is formed in between the parallel wires and the insulation surrounding the wires forms a bulge or cylindrical crest around the embedded wires. With conventional sharp pointed insulation displacement contacts, the contacts are dimensioned such that the sharp points engage the flat web between the parallel cylindrical crests. The edges extending inwardly from the sharp points, and between the sharp points and the insulation displacement slot, displace or penetrate the insulation surrounding the conductors, which are funneled into the slot where the primary electrical connection is established. Such insulation displacement terminations have proven to be very successful for typical ribbon cables which employ relatively small signal conductors.
The sharp points used on insulation displacement terminals intended for use with flat cables have also been employed in certain applications in which insulation displacement terminals are intended for use with discrete wires. For example, U.S. Pat. No. 4,527,852 discloses an electrical connector employing a U-shaped insulation displacement terminal in which the insulation displacement slot tapers from a mouth to a pair of opposed teeth positioned so that they point in the general direction of the mouth and serve to initiate severing of the conductor coating. U.S. Pat. No. 4,743,208 discloses another insulation displacement terminal intended for use with discrete wires in which finger portions extend upwardly from the plate portions containing the insulation displacement slots so that the height of the slot is greater than would otherwise be provided in an insulation displacement terminal having a strap portion adjacent the wire receiving mouth of the terminal.
Although these insulation displacement terminal configurations have been reliably employed to establish electrical connection to discrete conductors and to flat cable using mass termination techniques, none of these insulation displacement terminals have been specifically adapted for use with a hybrid ribbon cable. A hybrid ribbon cable is defined as a cable having conductors of different sizes. For example, a hybrid ribbon cable has been proposed for use in house wiring in which twelve or fourteen gauge power conductors would be combined with twenty-four gauge signal conductors. If insulation displacement mass termination techniques are to be used to terminate such cables, the terminals terminating the power conductors must be larger than the terminals terminating the signal conductors. Prior art techniques, in which the insulation surrounding the conductors in a flat cable are initially penetrated by inclined edges defining a portion of the funnel shaped mouth of the insulation displacement slot, have proved unreliable in terminating these conductors. One problem that has been encountered is the displacement of the terminals themselves as they engage the insulation surrounding the conductors. FIG. 1 shows a prior art configuration in which the terminal arms are displaced, i.e. plastically deformed, by the insulation to the point that contact is not made with the conductor. Note that insulation remains between the conductor and terminal arms. Although this problem is especially significant with respect to the more fragile and flimsy small contacts used to terminate closely spliced signal conductors, the same problem can be encountered with the larger insulation displacement terminals intended for use in terminating relatively large power wires. The instant invention is especially adapted for terminating hybrid ribbon cables, but the terminals employed herein and the connector employed herein can also be used with discrete conductors. Simple and reliable termination which can be carried out in uncontrolled, field, applications is achieved by employing the terminals incorporating the subject matter of this invention.